The invention relates to thickening agents based on at least one synthetic phyllosilicate.
In liquid or flowable coating systems, such as paints, varnishes, adhesives, printing inks, undersealing compositions, drilling fluids, cosmetic and pharmaceutical formulations, phyllosilicates are used to solve a number of problems such as settling of heavy pigments or active agents during storage, making available the necessary layer thickness for protective reasons, making available the viscosity suitable for the particular application, etc.
These phyllosilicates can form thixotropic "house-of-card" structures which impart the desired properties to the systems. Since these products themselves have a strong thickening action, which is certainly the reason for their use, the materials are not offered or marketed in predispersed form. This is due mainly to the fact that only pastes having a solids content of 2 to 8% can be produced and handled as a suspension. With the product essentially comprised of water, transportation of the product is not economically feasible.
Moreover, too much water can be brought into the formulation. This can result in the desired thickening effect of the phyllosilicate being neutralized by the high additional amount of water.
Moreover, a good dispersion of powders is a problem with phyllosilicates. Either the dispersion is not complete and the material is only partially used, (this also leads to other problems such as seeds (coarse particles) formation, post-thickening phenomena, loss of gloss and efficiency), or the dispersion is not possible in the desired formulation as the result of a lack of water and thus the possibility of compensating for the lacking mechanical dispersion forces by swelling with water. Even if the necessary mechanical dispersion energy is available, in many cases dispersion cannot be completely effected, as the components of the formulation are not always shear-stable. Uncontrollable post-thickening effects are thus the result and in some circumstances also seed formation, agglomerates and loss of gloss.
The addition of dispersion agents to improve dispersion is known in the art. However, this addition is normally done only after the phyllosilicate has been prewetted in water. The phyllosilicate is generally prewetted because most dispersion agents are highly polar and thus, can become attached to the edges of the phyllosilicate lamellae, such that hydration is suppressed and the opposite effect from dispersion is achieved. Dispersion agents, for example, based on acrylate or acrylamide, have a tendency to flocculate suspensions. This naturally reduces the viscosity of a phyllosilicate gel and also results in poor delamination and dispersion.
A process for producing organophilic clays with improved dispersibility in organic liquids is known from U.S. Pat. No. 4 382 868, in which a mixture of a smectite clay, a quaternary ammonium or phosphonium compound, water and an alcohol with 1 to 5 carbon atoms is extruded and the resulting organoclay gelatinization agent is ground without removing the water or alcohol. The product is no longer a clay which is capable of swelling in water.
A flame-inhibiting lubricant is known from U.S. Pat. No. 5 128 067 which contains a mixture of alkoxy and phenyl triesters of a phosphorus oxy acid and a fine-particle silica-containing thickening agent, for example, clay and silica. However, it is not a conversion product.
Organophilic clays are known from U.S. Pat. No. 5 336 647 which discloses the reaction product of a smectite clay with a first organic cation and a second organic cation from a polyalkoxylated quaternary ammonium salt. The clay is no longer present in hydrophilic form.
A gel-forming organophilic clay is known from DE-C-3 145 452 which discloses the reaction product of a clay of the smectite type with an organic anion (for example, a phosphite or phosphate) and an organic cation, for example, a quaternary ammonium or phosphonium compound. The conversion product is no longer hydrophilic.
An agent for enhancing the viscosity in nonaqueous liquid phases is known from DE-A-3 914 916 which is formed from finely dispersed particles of an inorganic laminar compound with positive layer charge based on two dimensional inorganic polycations (polycationic laminar compounds) and mono- and/or polybasic acid anions of a pronounced oleophilic nature. This product is not capable of swelling in water.
A gel-forming organophilic clay is disclosed in DE-A-3 145 475, which represents the reaction product of an organic cation, an organic anion and a clay of the smectite type. The organic cation is chosen from the group of quaternary ammonium salts, phosphonium salts and/or sulfonium salts. This product is not capable of swelling in water.
Use of phosphoric acid esters and their salts as dispersion agents and dispersion stabilizers for pigments in dyes, paints, and synthetic resins is known from DE-A-3 930 687. Aluminum hydroxide, zinc stearate, calcium carbonate, magnesium oxide and carbon black are named as pigments.
Easily dispersible organosmectites are known from DE-C-3 230 476 which contains exchangeable cations which have been replaced up to 50% by organic cations and which contains a surface which is covered with a peptising agent which is chosen from the group of sodium tetrapolyphosphate, sodium tripolyphosphate, sodium silicate, pyrogallol, gallic acid, and tannate. This product is also no longer capable of swelling in water.
It is known from Kittel, Hans: Lehrbuch der Lacke und Beschichtungen (Textbook of Paints and Coatings), Verlag W.A. Colomb in H. Heenemann GmbH, Berlin-Oberschwandorf, 1974, volume II, pp. 340, 341 that silicates, for example, minerals of the montmorillonite type, can be used as additives for paints. No information is disclosed on the modification of these substances for purposes of better dispersibility.
Rheological additives or thickening agents for pigment-containing protective coatings are known from Van Doren, Robert E., et al.: "The Role of Rheological Additives in Protective Coatings"; Journal of Protective Coatings and Linings, May 1989, pp. 47-52. Among those disclosed are pyrogenic silicic acids, cellulose-containing thickening agents, acrylates, and polyester-polyurethanes.
The objective of the invention is therefore to improve the dispersibility of phyllosilicates such that a powdered material can be easily dispersed at low to medium shearing forces without seeds. Another object is to provide pumpable pastes which can be easily metered and in which the phyllosilicate is present in completely dispersed form.